1. Field of the Invention
The present invention relates to a method, a dressing and a dressing assembly for detecting a leak between the dressing and an electrically conductive object by measuring the changes in capacitance between the dressing and the electrically conductive object.
2. Description of the Related Art
Some stoma patients experience problems with leakage from ostomy bags or leakage of body fluids from the ostomy. Origins of the leakages can be skin folds developed underneath the adhesive of a bandage, a scar near a stoma not providing good adhesion or presence of a humid spot prior to attaching the adhesive and thereby preventing the adhesive from obtaining good adhesion to the skin or the leak may occur in time as the adhesive properties of the bandage deteriorate. A leakage for a stoma patient can be embarrassing and highly inconvenient. Also wound care patients can have problems with leakages from a dressing. A patient may withdraw from social contact because of the smell or the sight of exudates leaking from a wound.
With an increasing elderly population in many countries, national health care systems have much focus on the total cost. For stoma patients or chronic wound patients, the bandages or the dressings are often changed regularly by a caring nurse. Extending the length of time a bandage or a dressing can remain on the stoma or wound reduces the need for care, enabling a reduction in health care costs.
An early warning reporting system either to the patient or to the caring nurse that a bandage or a dressing needs to be changed would therefore be useful. Not only will the patient avoid unpleasant accidents, helping the patient to feel confident and secure in his or her daily life, but it may also reduce the cost of our health care systems.
There is therefore a need of a sensor, which is able to report to the patient himself or herself or to a caring nurse, when leakage starts to occur in a bandage or a dressing and it needs to be changed. However, it is important that the sensor triggering such an alarm has a high degree of reliability, i.e. essentially no false negative alarms, and that it can provide a fast response enabling the patient or the nurse sufficient time to change the bandage or the dressing.
U.S. Pat. No. 4,754,264 discloses a water detecting device for a diaper based on sensing the degree of wetness by positioning two capacitor electrodes in the diaper detecting a liquid being absorbed by a water permeable sheet covering the two electrodes. The water permeable sheet causes a change in the dielectric constant of the electrostatic capacitance between the two electrodes and a detecting circuit detecting a change of the electrostatic capacitance transmitting a signal indicating that the diaper is wet. The U.S. Pat. No. 4,754,264 makes use of the fact that a medium comprising a water absorbing material gets wet, but the water has flown from the source to the permeable sheet, before it gets absorbed. It is therefore not suitable to detect a leak before it has wetted the medium.
WO02/099765 discloses a resonance circuit arranged on an insulating substrate with at least one pair of spaced measuring electrodes arranged in parallel or in series with the resonance circuit in such a manner that a material able to change its electrical conductivity under external influence can be placed or can pass through in the space between the measuring electrodes. Measuring the change of the resonance frequency or the Q-factor of the resonance circuit permits measuring and surveying the electrical conductivity of a material and measure changes under external influence such as e.g. moisture and temperature. However, the invention makes use of a change in the electrical conductivity and the material to be measured needs to be placed between the two measuring electrodes. This method is therefore not suitable for detecting a leak at the interface between the skin and an adhesive, because this interface cannot in a practical way be placed between two measuring electrodes.
EP 1 188 157 discloses a radio frequency resonant circuit sensing device for detecting a fluid in an article or container, in particular a body fluid from a human or an animal. The device comprises a layered structure with two electrically conducting electrodes attached to a substrate and with a dielectric medium in between the two electrodes. The resonant circuit sensing device is contained within the article to be measured. The invention can be suitable for measuring if a wound bleeds or a stoma bag is filled. However, the body fluid to be measured needs to be guided to the space between the two electrically conducting electrodes. It is therefore not suitable for detecting a leak due to exudates of a wound or discharge from a stoma propagating between the skin and an adhesive to the periphery of a bandage or dressing.
GB 2 343 628 discloses a device measuring the conductivity of the adhesive of a seal for an ostomy bag. The measuring device comprises two series of microelectrodes arranged on two tracks of at least an arc of a circle whose centre is coincident with the centre of a through-passage to an ostomy. The microelectrodes have substantially the form of a small cylinder of metal and penetrate to about half the thickness of the adhesive composition. It is thus the conductivity of the adhesive between the two series of electrodes, which is measured.
However, such a device measuring the conductivity of the adhesive only makes a respond in the case, where the adhesive has lost its effectiveness and it is desirable to change the adhesive. Furthermore, as the device measures directly between the two series of electrodes, the device will not detect a leak occurring as a consequence of a skin-fold, a scar or a wet spot creating a channel for a leak and where a leak propagates between the skin and the adhesive.
There is therefore a need in the art of sensors of being able to detect leaks around the whole periphery of a stoma or a wound propagating between the skin of a person and the adhesive of a bandage or a dressing in sufficient time before such a leak has propagated to the edge of the bandage or dressing.
An objective of the present invention is to provide a sensor detecting a leak between an adhesive of a bandage or dressing and the skin of a person or any other mammal making use of the skin as a ground plane for an alternating electrical current at frequencies, where the skin has a moderate or high conductivity.
Another objective of the present invention is to detect the leak in ample time before it has propagated completely to the edge of the bandage or dressing.
A further objective of the present invention is to provide sensitivity at the whole periphery of a stoma or a wound.
An even further objective of the present invention is to provide a sensor, which may be produced at high production throughput and at low cost.
An even further objective of the present invention is to provide a sensor which is disposable and which may be connected to a reader unit in a simple way.
An even further objective of the present invention is to provide a sensor reporting the condition of the adhesive of a bandage or a dressing of a wound to a patient, a caring nurse or a service centre.